Damaged Gelcoat below waterline on Westerly Centaur

[Swanrad2]

HI,

We neglected our Keel bolts. They became loose towards the end of the season and when bringing ashore the keel flexed cracking the gelcoat over a couple of square metres beneath the antifoul. So, I need to grind it back and have been watching videos and reading blogs for a few days but thought I would check my conclusions with the great hive mind.

1. I am intending to grind the gel-coat back to fibreglass (test grinds have revealed the cracks do not extend into the underlying laminate which is sound and not discoloured) one small section at a time, say 6 inches x 6 inches to catch all of the cracks. For this I think a flap wheel on an angle grinder seems to make most sense, done slowly and carefully so as not to grind too deeply into the glass.
2. Wash down with denatured alcohol.
3. Assuming no damage to any of the laminate I may lay on a couple of layers of bi-axial glass with epoxy resin to secure the substrate.
4. Sand back slightly and use gel-coat to 'bridge' between the high points to either side of the 'trench' I have ground out.
5. Repeat.

I have no experience of Epoxy based fillers, hence I'm reverting to gel coat. I own an angle grinder (but not a long nose sander that some of the videos seem to favour) so that seems to make sense.

Am I missing anything?

Cheers

 

[john_morris_uk]

HI,

We neglected our Keel bolts. They became loose towards the end of the season and when bringing ashore the keel flexed cracking the gelcoat over a couple of square metres beneath the antifoul. So, I need to grind it back and have been watching videos and reading blogs for a few days but thought I would check my conclusions with the great hive mind.

1. I am intending to grind the gel-coat back to fibreglass (test grinds have revealed the cracks do not extend into the underlying laminate which is sound and not discoloured) one small section at a time, say 6 inches x 6 inches to catch all of the cracks. For this I think a flap wheel on an angle grinder seems to make most sense, done slowly and carefully so as not to grind too deeply into the glass.
2. Wash down with denatured alcohol.
3. Assuming no damage to any of the laminate I may lay on a couple of layers of bi-axial glass with epoxy resin to secure the substrate.
4. Sand back slightly and use gel-coat to 'bridge' between the high points to either side of the 'trench' I have ground out.
5. Repeat.

I have no experience of Epoxy based fillers, hence I'm reverting to gel coat. I own an angle grinder (but not a long nose sander that some of the videos seem to favour) so that seems to make sense.

Am I missing anything?

Cheers

I think you’re missing a trick by dismissing epoxy. It’ll stick better and be stronger than the ‘gel coat’ your suggesting. Gel coat adds no real strength to the structure in itself and is certainly not suitable for wetting out the mat you say you might use. Polyester resin won’t bond half as well to the existing structure as epoxy will.

Get one of the packs with pumps that meter the proportions and you can’t go wrong. Either that or get some cheap digital scales and cover them with cling film and weigh out the quantities of epoxy and hardener.

Use gloves.

 

[Old Harry]

I think you’re missing a trick by dismissing epoxy. It’ll stick better and be stronger than the ‘gel coat’ your suggesting. Gel coat adds no real strength to the structure in itself and is certainly not suitable for wetting out the mat you say you might use. Polyester resin won’t bond half as well to the existing structure as epoxy will.

Get one of the packs with pumps that meter the proportions and you can’t go wrong. Either that or get some cheap digital scales and cover them with cling film and weigh out the quantities of epoxy and hardener.

Use gloves.

Hempel epoxy is also easy to use

 

[Swanrad2]

I think you’re missing a trick by dismissing epoxy. It’ll stick better and be stronger than the ‘gel coat’ your suggesting. Gel coat adds no real strength to the structure in itself and is certainly not suitable for wetting out the mat you say you might use. Polyester resin won’t bond half as well to the existing structure as epoxy will.

Get one of the packs with pumps that meter the proportions and you can’t go wrong. Either that or get some cheap digital scales and cover them with cling film and weigh out the quantities of epoxy and hardener.

Use gloves.

I was going to use epoxy on the wetting out bit...I just assumed the gel coat would adhere to the new laminate and the epoxy would adhere to the old glassfibre. So you would suggest - epoxy/glass and then epoxy/micro-beads (or something else) for fairing instead of gel coat?

 

[Rappey]

Is it just hairline cracks running around?
Why not just grind along the cracks with an angle grinder ,epoxy fill and paint?

 

[Catalina36]

Is it just hairline cracks running around?
Why not just grind along the cracks with an angle grinder ,epoxy fill and paint?

Until they're ground out you couldn't be certain they didn't extend any deeper. For peace of mind I'd want to get to the bottom of it, not start to wonder on some dark night whether my keels weren't secure.

 

[Catalina36]

HI,

We neglected our Keel bolts. They became loose towards the end of the season and when bringing ashore the keel flexed cracking the gelcoat over a couple of square metres beneath the antifoul. So, I need to grind it back and have been watching videos and reading blogs for a few days but thought I would check my conclusions with the great hive mind.

1. I am intending to grind the gel-coat back to fibreglass (test grinds have revealed the cracks do not extend into the underlying laminate which is sound and not discoloured) one small section at a time, say 6 inches x 6 inches to catch all of the cracks. For this I think a flap wheel on an angle grinder seems to make most sense, done slowly and carefully so as not to grind too deeply into the glass.
2. Wash down with denatured alcohol.
3. Assuming no damage to any of the laminate I may lay on a couple of layers of bi-axial glass with epoxy resin to secure the substrate.
4. Sand back slightly and use gel-coat to 'bridge' between the high points to either side of the 'trench' I have ground out.
5. Repeat.

I have no experience of Epoxy based fillers, hence I'm reverting to gel coat. I own an angle grinder (but not a long nose sander that some of the videos seem to favour) so that seems to make sense.

Am I missing anything?

Cheers

"We neglected our Keel bolts. They became loose towards the end of the season and when bringing ashore the keel flexed."

I'm a bit puzzled as to how they came loose this far into the life of the boat, given that Centaurs haven't been built for 40 years. They wouldn't normally just come undone. Are you sure you didn't hit something previously? If so, and enough to cause the keel to come loose, I'd doubt that the damage is limited to some cracked gelcoat. Alternatively, are you sure the bolts haven't wasted?

Not my business but I'd want to get right to the bottom of that.

 

[pvb]

We neglected our Keel bolts. They became loose towards the end of the season and when bringing ashore the keel flexed cracking the gelcoat over a couple of square metres beneath the antifoul.

Westerly Centaurs are prone to keel problems. Many of them have been reinforced with extra layers of glass and tranverse stiffening webs. Has yours been modified? If not, you ought to get it done.

 

[pvb]

1. I am intending to grind the gel-coat back to fibreglass (test grinds have revealed the cracks do not extend into the underlying laminate which is sound and not discoloured) one small section at a time, say 6 inches x 6 inches to catch all of the cracks. For this I think a flap wheel on an angle grinder seems to make most sense, done slowly and carefully so as not to grind too deeply into the glass.
2. Wash down with denatured alcohol.
3. Assuming no damage to any of the laminate I may lay on a couple of layers of bi-axial glass with epoxy resin to secure the substrate.
4. Sand back slightly and use gel-coat to 'bridge' between the high points to either side of the 'trench' I have ground out.
5. Repeat.

Doing it in tiny sections doesn't sound like an appropriate method. You'll get a more consistent result if you grind out all the cracks and then tackle the rectification in one go.

 

[Rappey]

Swanrad2 also said test grinds have revealed the cracks do not extend into the underlying laminate which is sound and not discoloured , which is why I offered a quick fix idea .
At the same time cracking gel coat over a few square meters is a surprise as I would have thought the damage would be more localised.

 

[pvb]

At the same time cracking gel coat over a few square meters is a surprise as I would have thought the damage would be more localised.

Westerly production control wasn't very sophisticated, and the gelcoat is often excessively thick. This can lead to it becoming brittle and cracking more easily when flexed.

 

[neilf39]

Are you saying one of the keels has come visibly loose so one side dug into the fibreglass on one side when either in the air or put down on the keel, hence the cracks? If so then you should have a gap around the keel where the bedding has given up. Did you see the keel move and have you tightened up the bolts? The alternate is the keel bolts were not loose and the hull has actually flexed, and as stated before, some Centaurs that lived on mud berths flexed as the matrix/frames around the keel were not beefy enough. How sure are you there is no damage to the fibreglass? Does anything look amiss around the keel bolts or along the hull/ribs internally? Looking back you mentioned keel in the singular. Is it one keel of a bilge keel that is affected, or both, or do you have a fin keel (If so it's a Pembroke, not a Centaur). Is the cracking at the front or back of the keel or all along/around it? I think we need a bit more clarification and maybe some photos.

 

[Rappey]

The alternate is the keel bolts were not loose and the hull has actually flexed

I thought that as another possibility but didn't get it into words

 

[Rappey]

This can lead to it becoming brittle and cracking more easily when flexed

Boat breakers in Portsmouth have an articLe about how grp at 30 yrs becomes dried out and brittle compared to newer and flexible grp.

 

[pvb]

Boat breakers in Portsmouth have an articLe about how grp at 30 yrs becomes dried out and brittle compared to newer and flexible grp.

Yes, age makes it more brittle too. So the OP's 40 year old Westerly may have quite brittle gelcoat.

 

[Swanrad2]

Are you saying one of the keels has come visibly loose so one side dug into the fibreglass on one side when either in the air or put down on the keel, hence the cracks? If so then you should have a gap around the keel where the bedding has given up. Did you see the keel move and have you tightened up the bolts? The alternate is the keel bolts were not loose and the hull has actually flexed, and as stated before, some Centaurs that lived on mud berths flexed as the matrix/frames around the keel were not beefy enough. How sure are you there is no damage to the fibreglass? Does anything look amiss around the keel bolts or along the hull/ribs internally? Looking back you mentioned keel in the singular. Is it one keel of a bilge keel that is affected, or both, or do you have a fin keel (If so it's a Pembroke, not a Centaur). Is the cracking at the front or back of the keel or all along/around it? I think we need a bit more clarification and maybe some photos.

The boat lives on a mud berth over sand so dries twice a say, I suspect that this 'worked' the bolts slightly loose over time. By loose I mean not tightened to the required torque settings. We rectified this when launching but did not notice any cracking at this time. It was when laying up we noticed one of the keels was loose. Inside around the keel bolts and outside beneath the gel coat the glass looks to be perfect - no signs of cracking or discolouring. The cracks in the gelcoat are long and radiate out from the centre of the keel to the front and about two thirds of the way to the back in a flattened semi-circular pattern but do not extend into the glass itself. They were not there last year when we antifouled, or at least we did not notice them. All of the ribs are still attached and undamaged. The keel is now 'solid' with no flex when lowered to the ground at the beginning of last winter. Similarly there are no cracks in the gelcoat on the inside of the keel.

I do not think the keel 'dug in' to the gelcoat, I think the keel was being splayed when it dried and when it was laid up causing slight deflection of the glass in the hull which caused the gelcoat to crack. At no time was there any water ingress through the keel bolts into the hull (at least not enough to notice). A Centaur owner and the yard manager who have done this job before had a quick look at the weekend and agreed with my assessment. Both had re-built the shoes on Centaurs in the past and seen the damaged variety. But I am between trips to the boat and need to get the 'stuff' ordered for the job.

I was struggling to track the cracks with an angle grinder - is there a better way to do this?

Our intention is to drop the keel at the end of this 'season' and re-bed (we were originally going to be doing this before we launched but wet/windy winter and Covid messed that plan up. We are moving from the drying mooring for this season as well so less load on the keels. I will try to get some photo's next weekend with the area stripped back and some of the cracks ground back to the glass.

Hopefully this makes sense...

Finally, I don't think we hit anything last season, with that kind of damage to the gel coat I am pretty sure we would have noticed.

 

[Swanrad2]

Westerly production control wasn't very sophisticated, and the gelcoat is often excessively thick. This can lead to it becoming brittle and cracking more easily when flexed.

I tried to answer everyone's questions in my last comment but missed this one....the gel coat is thicker than I would have expected.

And.....thanks everyone for your comments!

 

[pvb]

Has your boat had the modification to strengthen the keel fixing?

 

[neilf39]

If it is a radiating pattern then it would imply to me that the centre of the pattern was the place that took the force and deformed. Is the centre of the flattened circle where the keel is the widest? I think if the keel was a bit loose then as it splayed out a bit as the boat settled the widest bit of the top of the keel would concentrate the force there to give the radiating pattern. Maybe there was enough flex in the fibreglass to not damage it but create the gel coat cracking. If so then just grinding the cracks and filling with epoxy filler would be ok.

 

[Graham376]

Has your boat had the modification to strengthen the keel fixing?

+1

Centaurs lose keels when the bottom falls out of the stub, usually the exact shape of the keel top. From what's been said, the keel needs to come off and the internal area needs cleaning off and reinforcing with small bulkheads across the stubs, the new layup needs to be carried well outside the stubs. The outside needs grinding back over the complete area to the depth of the cracks and may need some extra layup as well. I had to reinforce the stubs on a Berwick which is the same design, fortunately before the keels fell off.